The use of fire-retardant compositions to prevent and suppress flame intensity and rate of spread in wildland fires has been known since the 1950s. It should be understood that there are both short-term and long-term fire-retardants. Short-term retardants, also called suppressants or water enhancers, depend entirely on their contained water to cool the fire. Once their contained water evaporates, they are no longer effective. Water, itself can be considered a short-term retardant or suppressant. Bentonite clay and super absorbent polymers (SAP) are formulated examples of short-term retardants that are more effective than water because they are generally viscous and, consequently tend to remain where applied whereas liquid water runs off of the fuel onto the ground. Long-term fire-retardants, on the other hand, convert wildland vegetation from a substance that is flammable and, consequently, a fuel, to a substance that has been chemically modified or converted to a substance that does not ignite and provide fuel when heated to and beyond its ignition point by the advancing fire. Ammonium phosphate based long-term fire-retardants are the subject of this technology. They function by reacting with the fuel, converting it to a substance that does not release flammable gases when heated, but rather, decomposes to a graphic-like carbon via dehydration. This type of retardant is effective until it is removed from the vegetative fuel by either rain or some physical means. Many different types of long-term fire-retardants have been used, for example, sodium calcium borate, monoammonium and diammonium orthophosphate, diammonium sulfate, and aqueous solutions of ammonium polyphosphates that contains a mixture of ortho, pyro, and short chain polyphosphates. Ammonium phosphates are the long-term retardants specified by many agencies with responsibility for the prevention and management of wildland fire.
Fire-retardant application can be made from either aerial or ground vehicles, e.g., fixed-wing aircraft, rotatory wing aircraft (e.g., helicopters), and ground engines. Aerial attack is most commonly used when the fire is in areas not easily or quickly accessible from the ground. Typically, fire-retardants are supplied to the user as a dry or liquid concentrate which is subsequently mixed with water to form a solution containing a prescribed amount of fire-retardant concentrate per unit volume before or during loading the fire-retardant solution into the application vehicle. The prescription for the solution is determined by performance criteria when subjected to a standard fire test.
Fire-retardant solutions applied to fuels threatened by fire may accidently reach streams, rivers, lakes, ponds, and other waterways and wetland habitats. Consequently, it is desirable that fire-retardant solutions exhibit low aquatic toxicity. Since ammonia is toxic to many aquatic species, it is desirable that the fire-retardant solution contain a low ammonia content, consequently, there remains a need for fire-retardant solutions that contain reduced amounts of ammonia per unit volume.